An aluminum heat exchanger is comprised of an aluminum alloy fin material brazed to an aluminum material forming working fluid passages and the like. To improve the performance characteristics of the heat exchanger, as basic characteristics of this aluminum alloy fin material, a sacrificial anode effect has been demanded in order to prevent corrosion of the material forming the working fluid passages. Further, to prevent deformation due to high-temperature brazing heating and penetration of the brazing material, a superior sag resistance and erosion resistance have been demanded.
The fin material, in order to satisfy the above basic characteristics, has Mn and Fe added to it. Recently, however, effort has been focused on the production process and aluminum alloy fins for heat exchangers with a low tensile strength before brazing and a high tensile strength after brazing have been developed.
Japanese Patent Publication (A) No. 2005-220375 discloses a method of production of an aluminum alloy fin for a heat exchanger having a tensile strength before brazing of 240 MPa or less and a tensile strength after brazing of 150 MPa or more comprising pouring a melt containing Si: 0.8 to 1.4 wt %, Fe: 0.15 to 0.7 wt %, Mn: 1.5 to 3.0 wt %, and Zn: 0.5 to 2.5 wt %, limiting Mg as an impurity to 0.05 wt % or less, and having a balance of normal impurities and Al, continuously casting a thin slab of a thickness of 5 to 10 mm by a twin-belt casting machine, taking it up in a roll, then cold rolling it to a sheet thickness of 0.05 to 0.4 mm, process annealing the sheet at 350 to 500° C., and cold rolling it by a cold rolling reduction of 10 to 50% to a final sheet thickness of 40 to 200 μm.
On the other hand, a method of production of a heat exchanger has been developed which obtains a predetermined strength by defining the cooling rate after brazing when brazing an aluminum alloy fin material to an aluminum material forming working fluid passages.
Japanese Patent Publication (A) No. 1-91962 discloses a method of production of a heat exchanger taking note of the cooling rate after brazing heating and obtaining fins with a large tensile strength after brazing heating. Specifically, this is a method of production of a heat exchanger fabricating an Al heat exchanger by brazing during which performing the cooling from the brazing temperature to 350° C. by a cooling rate of 100° C./min to 1000° C./min so as to obtain fins of a large tensile strength.
Japanese Patent Publication (A) No. 2-142672 discloses a method of production of an aluminum heat exchanger obtained by stacking tubes and fins, attaching headers to both ends of the tubes, and brazing the pieces using a chloride-based flux in the atmosphere, in dry air, or using a fluoride-based non-corrosive flux in an inert gas atmosphere, said method of production of an aluminum heat exchanger characterized by using a brazing sheet to fabricate tubes with an outer surface comprised of an Al—Si-based alloy brazing material and with an inner surface comprised of an Al—Zn-based alloy and cooling from 500° C. to 200° C. after brazing them together at a rate of 50° C./min or more.
However, said Japanese Patent Publication (A) No. 2005-220375 has a description regarding the electrical conductivity after brazing heating (thermal conductivity), but no description particularly relating to the cooling rate after the brazing heating can be found.
Further, said Japanese Patent Publication (A) No. 1-91962 and Japanese Patent Publication (A) No. 2-142672 disclose art defining the cooling rate after brazing heating to obtain a high strength fin material, but no description relating to the electrical conductivity (thermal conductivity) after the brazing heating can be found.
Further, recently, to make the fin material thinner, development of an aluminum alloy fin material with not only the basic brazing characteristics, but also a high yield strength after brazing and superior in thermal conductivity after brazing has been hoped for.